Process for preparing hydroquinones

ABSTRACT

A one-step reductive hydrolytic method for preparing hydroquinone from p-nitrosophenol is disclosed. Good yields of hydroquinone are obtained by heating pnitrosophenol in a hydrogen atmosphere between 60* C - 150* C with a hydrogenation catalyst in an acid medium in the presence of an inert solvent.

United States Patent Doering et al.

[ 51 July 11,1972

[54] PROCESS FOR PREPARING HYDROQUINONES [72] Inventors: William Von E.Doering, Cambridge,

Mass.; William J. Farrissey, Jr., Northford; Floro F. Frulla,Wallingford, both of Conn.

[73] Assignee: The Upjohn Company, Kalamazoo, Mich.

[22] Filed: April 16, 1970 [21] Appl. No.: 29,280

[52] 0.8. Cl ..260/621 I1, 260/621 R [5 1 ..C07c 39/02 [58] Field ofSearch ..260/621 H, 621 R [56] References Cited UNITED STATES PATENTS3,395,160 7/1968 McLean ..260/6211-1 OTHER PUBLICATIONS Matsumura etal., J .A.C.S. 53 pp. 1406- 1408, 1931.

Primary Examiner-Howard T. Mars Attorney-Denis A. Firth and John Kekich[57] ABSTRACT A one-step reductive hydrolytic method for preparinghydroquinone from p-nitrosophenol is disclosed.

Good yields of hydroquinone are obtained by heating pnitrosophenol in ahydrogen atmosphere between 60 C 150 C with a hydrogenation catalyst inan acid medium in the presence of an inert solvent.

6 Claims, No Drawings PROCESS FOR PREPARING IIYDROQUINONES BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to anovel process for preparing hydroquinone from p-nitrosophenol. Moreparticularly, this invention relates to a one step reductive hydrolysisof. pnitrosophenol to the corresponding hydroquinone.

2. Description of the Prior Art The bulk of commercially availablehydroquinone is produced by reduction of benzoquinone, which is firstprepared by oxidation of aniline using, for example, manganese dioxide.U.S. Pat. No. 3,395,160 (McLean) discloses a two-step method forconverting p-nitrosophenol to hydroquinone. In the first step thep-nitrosophenol is heated between 150 C 200 C with a carbonyl compoundin acid media to yield p-benzoquinone. The second step is reduction ofthe pbenzoquinone with a reducing agent or by catalytic hydrogenation.

It was also known heretofore to prepare hydroquinone directly fromp-nitrosophenol by reduction of the latter with iron filings in acid.(Matsumura et al., J.A.C.S., Volume. 53, Pg. 1406). This method provideslow yields and is not commercially desireable for a variety of reasons,but particularly because the desired product must be separated from acomplex sludge of iron salts.

We have found that hydroquinone can be prepared directly from thecorresponding p-nitrosophenol in a one step process of reductivehydrolysis employing a catalytic hydrogenation technique. By our methoddisclosed herein, good yields of hydroquinone are obtained. Further, thehydroquinone is easily and economically separated from the reactionmixture in pure form using standard techniques.

SUMMARY OF THE INVENTION This invention comprises a process forpreparing hydroquinone, which process comprises subjectingpnitrosophenol to hydrogenation at a temperature within the range ofabout 60 C to about 150 C in an aqueous acidic medium in the presence ofan inert organic solvent and a hydrogenation catalyst which is stable inacid media, the amount of p-nitrosophenol present in the initialreaction mixture being not more than about grams per liter of saidmixture.

Hydroquinone is a well known compound which is useful as a photographicdeveloper, antioxidant, polymerization inhibitor, and as an intermediatein a number of organic chemical syntheses (Kirk-Othmer, Encyclopedia ofChemical Technology, 2nd edition, Vol. II pps. 4889).

DETAILED DESCRIPTION OF THE INVENTION The aqueous acid medium employedin the process of the invention comprises an aqueous solution of mineralacid. Illustrative of the mineral acids employed are sulfuric acid,phosphoric acid, hydrochloric acid and the like; preferably the mineralacid is sulfuric acid. The concentration of acid used can be from 0.1 Nto 6 N and preferably is from 0.5 N to 3 N. The amount of acid soemployed is important. Thus it is essential that the reaction mixture bemaintained acid throughout the reaction period. This is accomplished byproviding acid in an amount corresponding to at least one equivalent permole of the p-nitrosophenol charged in the reaction mixture. Preferably,an excess of acid is employed, the preferred amount of acid beinggenerally of the order of about 2 equivalents per mole of thep-nitrosophenol charged. The inert organic solvents employed in theprocess of the invention can be any of those organic solvents,substantially immiscible with water, which assist in solubilizingp-nitrosophenol, but do not themselves enter into the reaction ie. donot undergo any significant amount of hydrogenation under the conditionsof the reaction or otherwise interfere in the desired course of thecyclohexanone, and the like. A particularly preferred solvent is butylacetate.

The amount of inert organic solvent present in the reaction mixture isadvantageously not greater in volume than the volume of aqueous acidicmedium. Preferably the inert organic solvent is employed in an amountsuch that it constitutes about 10 percent to about 40 percent of thetotal volume of the reaction mixture. The amount of p-nitrosophenolemployed as starting material in the process of the invention iscritical insofar as the ultimate yield of hydroquinone is concerned.Thus we have found that the maximum amount of pnitrosophenol present inthe initial reaction mixture is of the order of 5 grams per liter, basedon total volume of the reaction mixture. The use of amounts ofp-nitrosophenol in excess of this maximum results in significantreduction in yield. Provided the above maximum is not exceeded, theprecise concentration of p-nitrosophenol employed is not important.

The hydrogenation catalyst employed in the process of the invention canbe any conventional catalyst usually used to catalyze the hydrogenationof an organic compound, subject to the requirement that it be stable inthe acid medium. Examples of such catalysts include the noble metals, ofwhich platinum and palladium are preferred. Supported catalysts such asplatinum-on-carbon, palladium-on-carbon and palladium-on-barium sulfateare particularly preferred. Platinumon-carbon is the most preferredhydrogenation catalyst.

The concentration of catalyst required is dependent upon the pressure ofhydrogen present during hydrogenation. In general, higher hydrogenpressures enable the reaction to proceed favorably with lower catalystconcentrations. For example when hydrogen is employed at atmosphericpressure up to 15 psi above atmospheric pressure, the catalystconcentration is preferably within the range of about 5 percent to about30 percent by weight of p-nitrosophenol. When hydrogen pressures ofabout 15 to 50 psi above atmospheric are employed, the preferredcatalyst concentration is from about 2 percent to about 5 percent byweight of p-nitrosophenol.

The process of the invention is carried out at a temperature within therange of from about 60 C to 150 C, preferably from C to C. Throughoutthe reaction period the mixture is vigorously agitated usingconventional apparatus and hydrogenation techniques.

Although the reaction proceeds satisfactorily over a wide range ofhydrogen pressures, it is preferable to employ a hydrogen pressure offrom about 15 to 50 psi above atmospheric so as to reduce the quantityof catalyst required, as previously stated.

Reaction is generally complete in about 1 to 3 hours, and completion ofthe reaction can be defected by standard analytical techniques such asthose employing vapor phase chromatography, gel permeationchromatography, infrared and ultra violet analytical techniques.

The hydroquinone is easily separated from the reaction mix ture usingconventional techniques and apparatus. For example, a convenientseparation can be performed by filtering the reaction mixture to removesolids, separating the organic layer and extracting the aqueous layerwith such solvents as diethyl ether, ethyl acetate, and the like. Thecombined organic layer and solvent extract are washed, dried andevaporated. The hydroquinone which remains as residue can be furtherpurified, if desired, by recrystallization from hot water, ether, ethylacetate, ethyl alcohol and the like solvents.

The following examples describe the manner and process of making andusing the invention and set forth the best mode contemplated by theinventors of carrying out the invention but are not to be construed aslimiting.

EXAMPLE 1 To a Parr low pressure catalytic apparatus is charged l.llgrns (9.04 millimoles) of p-nitrosophenol, 50.6 mg. of 1 percentplatinum-on-carbon (Baker Chemical Co.) 200 cc of l N sulfuric acid, and50 cc butyl acetate.

The reactor vessel is purged with hydrogen gas and charged additionallywith hydrogen gas at 50 psig. The mixture is heated between 95 C to 99 Cfor about 1 hour during which time it is vigorously agitated. Thereafterit is cooled and the mixture filtered to remove catalyst and residue.The organic layer is separated and the aqueous layer of the filtrate isextracted 3 times with 200 ml. portions of ether The combined organiclayer and extracts are washed with a solution of saturated sodiumchloride, dried over anhydrous magnesium sulfate and heated to evaporatesolvent. The residue is 0.68 grns of light tan crystalline needlesidentified by vapor phase chromatography as 71 percent hydroquinone (49percent theoretical yield). Recrystallization from benzene yields paleyellow crystalline needles of purified hydroquinone.

EXAMPLE 2 To the apparatus of Example 1 is charged 1.15 gms (9.36millimoles) of p-nitrosophenol, 37.5 mg of 1 percent platinum-on-carbon,150 cc of L5 N sulfuric acid and 100 cc of butyl acetate. The reactorvessel is purged with hydrogen gas and charged additionally withhydrogen gas to psig. The mixture is heated between 98 C to 103 C forabout 1 hour during which time it is vigorously agitated. Thereafter itis cooled and the mixture filtered to remove catalyst and residue. Theorganic layer of the filtrate is separated and the 2 EXAMPLE 3 To asuitable 1 liter vessel fitted with Vibro mixer, Model E- l, (a poweragitating unit causing vertical vibration of a stirrer at a frequencycorresponding to the A. C. power supply; Chemapec Inc. Hoboken, N. J.,)there is charged 1.02 gms (8.25 millimoles) of p-nitrosophenol, 213 mg.of 1 percent platinum-on-carbon, 200 ml. of l N sulfuric acid and 50 ml.of butyl acetate.

The mixture is heated between 88 C to 91 C for about 1 hour whilehydrogen gas is passed over the vigorously agitated mixture. The mixtureis then cooled and filtered to remove solids. The organic layer of thefiltrate is separated and the aqueous layer is extracted four times with150 cc portions of ether. The extracts are combined, washed with asaturated solution of sodium chloride, and dried over anhydrous sodiumsulfate. Upon evaporation of ether, there is obtained 0.38 gms. ofreddish brown solids identified by vapor phase chromatography as 84.5percent hydroquinone. The organic layer previously separated isevaporated, yielding solids weighing 0.20

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gms which are identified by vapor phase chromatography as 57.5 percenthydroquinone. The combined crude hydroquinone (0.58 gm) isrecrystallized from benzene yielding 0.44 gms (48 percent theoreticalyield) of purified hydroquinone.

EXAMPLE 4 This example is not an example of the invention, butillustrates a prior known method (Matsumura et al. supra) for preparinghydroquinone directly from p-nitrosophenol.

To a hot (circa C) solution of 27 grns concentrated hydrochloric acid in1,050 ml. of water is added 2.5 gms (20.2 millimoles) p-nitrosophenol.While maintaining the temperature at circa 95 C, 5 gms (89.5 millimoles)iron powder is slowly added over a period of about 1 hour with constantagitation of the reaction mixture. The reaction mixture is maintained atcirca 95 C for an additional 1 hour with agitation and then filtered toremove residue. The cooled filtrate is extracted five times with 200 mlportions of ether. The extracts are combined dried over sodium sulfateand heated to evaporate solvent, yielding 1 gm of reddish brown solidswhich are identified by vapor phase chromatography as containing 20percent hydroquinone (9 percent theoretical yield).

What is claimed is:

l. A process for preparing hydroquinone which comprises:

subjecting p-nitrosophenol to hydrogenation at a temperature within therange of about 60 C to about C in an 0.l N to 6 N aqueous solution of amineral acid selected from the group consisting of sulfuric acid,phosphoric acid and hydrochloric acid and in the presence of an inertorganic solvent selected from the group consisting of ethyl acetate,butyl acetate, toluene, dibutyl ether, 0- xylene and cyclohexanone; saidinert solvent being present in a volume less than the volume of aqueousacid solution employed; and in the presence of from about 2 percent toabout 30 percent by weight of p-nitrosophenol of a noble metalhydrogenation catalyst which is stable in acid media; the amount ofp-nitrosophenol present in the initial reaction mixture being not morethan about 5 grams per liter of said mixture.

2. The process of claim 1 wherein said acid is sulfuric acid.

3. The process of claim 1 wherein said inert solvent is butyl acetate.

4. The process of claim 1 wherein said inert organic solvent constitutesfrom 10 percent to 40 percent by volume of the reaction mixture.

5. The process of claim 1 wherein said catalyst is platinumon-carbon.

6. The process of claim 1 wherein said catalyst is present in aconcentration of about 2 percent to about 5 percent by weight ofp-nitrosophenol and the hydrogenation is carried out at a pressure of 15psi to 50 psi above atmospheric pressure.

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2. The process of claim 1 wherein said acid is sulfuric acid.
 3. Theprocess of claim 1 wherein said inert solvent is butyl acetate.
 4. Theprocess of claim 1 wherein said inert organic solvent constitutes from10 percent to 40 percent by volume of the reaction mixture.
 5. Theprocess of claim 1 wherein said catalyst is platinum-on-carbon.
 6. Theprocess of claim 1 wherein said catalyst is present in a concentrationof about 2 percent to about 5 percent by weight of p-nitrosophenol andthe hydrogenation is carried out at a pressure of 15 psi to 50 psi aboveatmospheric pressure.